The means of communication between various floors is offered by various structures such as stairs, lifts, ramps, ladders, escalators.A stair is a series of steps arranged in a manner as to connect different floors of a building. Stairs are designed to provide an easy and quick access to different floors.
- A staircase is an enclosure which contains the complete stairway.
- In a residential house stair may be provided near the entrance.
- In a public building, stairs must be from main entrance and located centrally.
STAIRCASE: Room of a building where stair is located.
STAIRWAY: Space occupied by the stair.
SOME TECHNICAL TERMS FOR STAIRCASE
- BALUSTER: Vertical member which is fixed between stairway and horizontal to provide support to hand rail.
- BALUSTRADE: Combined framework of baluster and hand rail.
- STRING: Inclined member of a stair which supports ends of steps. They are of two types, (i) cut/open string, (ii) closed/housed string.
- In open string, upper edge is cut away to receive the ends of steps.
- In closed string, the ends of steps are laid between straight and parallel edges of the string.
- FLIGHT: Unbroken series of steps between the landings.
- GOING: horizontal distance between faces of two consecutive risers.
- HANDRAIL: inclined rail over the string. Generally, it is moulded. It serves as a guard rail. It is provided at a convenient height so as to give grasp to hand during ascent and descent.
- HEAD ROOM: vertical distance between nosing of one flight and the bottom of flight immediately above is called head room.
- LANDING: horizontal platform between two flights of a stair. A landing facilitates change of direction and provides an opportunity to take rest.
- NEWEL POST: vertical member placed at ends of flights to connect ends of string and hand rail.
- NOSING: projection part of tread beyond face of riser.
- LINE OF NOSING: imaginary line parallel to strings and tangential to nosing’s. The under face of hand rail should coincide with line of nosing.
- PITCH: angle of inclination of stair with floor.
Angle of inclination of line of nosing with horizontal.
- RISE: vertical distance between two successive treads.
- RISER: vertical member of the step, which is connected to treads.
- RUN: length of a stair in a horizontal plane which includes length of landing.
- SCOTIA: an additional finish provided to nosing to improve the elevation of the step which also provides strength to nosing.
- SOFFIT: under surface of a stair. Generally, it is covered with ceiling or finished with plaster.
- STEP: combination of trade and riser. Different types are.
- Commode steps: it has curved riser and tread
- Dancing step: they don’t radiate from a common centre
- Flier: ordinary step of rectangular shape in plan
- Round ended step: similar to bullnose step except that its ends are semi-circular in plan
- Splayed step: it has either one end/both ends splayed in plan
- Winder: this is a tapering step and is used to change the direction of a flight. The winders radiate from a common centre.
- Tread: horizontal upper portion of a step.
- Waist: thickness of structural slab in RCC stair
- Carriage: a rough timber supporting steps of wooden stairs
REQUIREMENT OF GOOD STAIRCASE
- Stairs should be so located that it is easily accessible from the different rooms of a building.
- It should have adequate light and proper ventilation.
- It should have sufficient stair width to accommodate no. of persons in peak hour/emergency.
Generally, for interior stairs, clear width may be
- at least 50cm in one/two family dwellings
- at least 90cm in hotels, motels, apartment and industrial building
- at least 1.1m for other types like hospitals, temples etc.
- No. of steps in a flight should be restricted to a maximum of 12, minimum of 3.
- Ample head room should be provided for tall people to give feeling of spaciousness. It should be minimum of 2.15m.
- Risers and treads sizes should be provided from common point view.
Tread = 2.5cm – 32.5 cm (wide), excluding nosing.
Tread < 25cm, should have a nosing of about 2.5cm
Comfortable height of riser = 17.5cm-18.5cm.
Riser * tread = (400-410). 426
Riser + tread = (42.5-43.5) 40-45
2(riser) + tread = 60-64 cm 60
Take rise = 14cm, going = 30cm.for each 2cm subtracted from going, add 1cm to rise.
- Stair width depends on purpose and importance of building.
- No. of stairways required should be controlled by maximum floor area contributory to stairway.
(No. of persons using stairs/floor/55cm stair width)
should be 15 for hospital and nursing home.
Should be 30 for institutional and residential building
Should be 45 for storage building
Should be 60 for mercantile, educational, industrial building, theatres, restaurants.
Should be 80 for church concert hall, museum
Should be 320 for stadium and amusement structures.
- Minimum width of landing = width of stair
- Maximum and minimum pitch should be 400 and 250.
- Winder should be provided at lower end of flight when it is essential. Use of winder should be avoided.
- Live load to be considers n stairs have been stipulated by IS 875-1964
- Stairs and landings should be designed for live load of 3000kg/m.s2 in building where there are no possibilities of overcrowding in public building and warehouses where overcrowding is likely live load may be taken as 500kg
- Railing should be design for horizontal force of 55 and vertical force of 70 applied at top of rail
DIFFERENT TYPES OF STAIRCASES
- Straight stair:
- Here there is no change in the direction of any flight between two successive floors.
- It can be straight run with a single flight between floors or a series of flights without change indirection Parallel stairs
- Straight stair can have a change in direction at any intermediate landing.
- In parallel stair, there is complete reversal of direction occurs.
- In angle stair, successive flights are at an angle to each other.
- Scissor stairs are comprised of a pair of straight runs in opposite direction and are placed on opposite sides of a fire resistivity wall.
- Turning stairs:
- Quarter turn stair:
- Provided where flight direction is to be changed by 900
- Change in direction can be affected by either introducing a quarter space landing or by providing winders at junctions.
- Half turn stair:
- They change their direction through 1800. They can be dog legged and open newel.
- In doglegged stair, flights are in opposite direction and no space is provided between the flights.
- In open newel stair, there is a well/opening between flights and may be used to accommodate lift.
- Open newel stairs are used at places where sufficient space is available.
- Three quarter turn stairs:
- They change in the direction through 2700 or direction is changed with its upper flight crossing the bottom one.
- In this type an open well is formed.
- Circular stair:
- When viewed from above, appear to follow a circle with a single centre of curvature and large radius.
- Generally, they are provided at the rear of a building to the access for serving at various floors.
- All the steps radiate from a newel post in the form of winders.
- Made up of stone, cast iron/RCC.
- Spiral stairs:
- Similar to previous one except that the radius of curvature is small and the stair may be supported by a centre post.
- Over all diameter ranges from 1-2.5m
- Curved stair:
- When view from above appear to follow a curve with 2 or more centre of curvature, such as ellipse.
- Geometric stair:
- They have no newel post are of any geometric shape.
- The change in direction is achieved through winders.
- They needs more skills for its construction and are weaker than open newel stairs
- Here the open well between forward and backward flights is curved.
- Bifurcated stair:
- So arranged that there is a wide at the start and subdivided into narrow flights at mid landing.
- The two narrow flights start from either side of mid landing.
- They are suitable for modern public buildings.
CLASSIFICATION OF STAIRS BASED ON MATERIALS OF CONSTRUCTION
General materials used in construction of stairs are
- Plane concrete
- Wooden stair
- As they are light in weight, mostly used for residential building.
- The main objection to this stair is that it is easily attacked by fire and thus, in fire, the occupants of upper floor can’t escape.
- If it is made from good timber like Teak, and thickness is about 45mm,it becomes sufficiently fire proof and allows enough time for occupants on upper floor to escape.
- The string supporting ends of wooden steps may be a cut string/closed string.
- Scotia blocks may be provided to give additional finish to wooden steps.
- Small triangular wooden blocks called glue blocks may be provided at inner angle formed between a trade and riser, to provide additional strength.
- A metal strip may be provided on nosing of wooden step to increase its resistance against wear and tear.
- The landing may be formed by providing wooden beams of suitable sizes.
- Sometimes risers are omitted. trades are housed in strings and soffit is covered with wooden battens/metal sheets.
- The timber used should be free from fungal decay, insect attack, or any defect. Edges may be finished smooth and excess light timber should not be used.
- Metal Stair
- They are not frequently/commonly used stairs.
- The external fire escape stairs are generally made of metal.
- Common metals are CI, bronze, and mild steel.
- Widely used in factories, workshop, and basement. Main features are,
- Stringers are usually of channel section
- Tread and riser of a step may be of one unit or may not be
- Tread and risers are supported on angles, which are connected to stringers.
- Risers may be totally omitted.
- Spirals stairs of CI consists of CI newel fixed in centre around which the CI steps are fixed.
- For metal stairs metal balusters with pipe handrail are used.
- RCC Stair
- Commonly used in all type of construction.
- They resist better fire and wear than any other material and can be moulded to desired shape.
- The step can be provided with suitable finishing material such as marble, terrazzo, tiles etc.
- They can be easily maintained, strong, durable and pleasing in appearance.
- They can be designed for greater widths and layer spans.
- The steps may cast in situ/pre cast.
- It is possible to pre cast a flight and place it in position by equipment.